Investment Securities - Unrealized Gross Losses and Fair Values of Securities in a Continuous Loss Position (Details) $ in Thousands	Jun. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Securities in the available-for-sale portfolio in a continuous loss position
Number of individual securities in a continuous loss position | security	16	118
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	$ (1,489)	$ (9,658)
12 Months or More Unrealized Losses	(79)	(14,329)
Total Unrealized Losses	(1,568)	(23,987)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value	415,512	1,314,806
12 Months or More Fair Value	18,025	994,155
Total Fair Value	433,537	2,308,961
Government-sponsored enterprises debt securities
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses		(277)
Total Unrealized Losses		(277)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value		49,716
Total Fair Value		49,716
Residential - Government agency
Time in Continuous Loss, Unrealized Losses
12 Months or More Unrealized Losses		(1,146)
Total Unrealized Losses		(1,146)
Time in Continuous Loss, Fair Value
12 Months or More Fair Value		109,614
Total Fair Value		109,614
Residential - Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses		(115)
12 Months or More Unrealized Losses		(1,558)
Total Unrealized Losses		(1,673)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value		76,481
12 Months or More Fair Value		109,025
Total Fair Value		185,506
Commercial - Government agency
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	(456)
Total Unrealized Losses	(456)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value	90,834
Total Fair Value	90,834
Commercial - Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses		(634)
Total Unrealized Losses		(634)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value		38,062
Total Fair Value		38,062
Government agency
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	(603)	(8,049)
12 Months or More Unrealized Losses	(52)	(8,299)
Total Unrealized Losses	(655)	(16,348)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value	200,395	969,762
12 Months or More Fair Value	9,212	565,764
Total Fair Value	209,607	1,535,526
Government-sponsored enterprises
Time in Continuous Loss, Unrealized Losses
Less Than 12 Months Unrealized Losses	(430)	(583)
12 Months or More Unrealized Losses	(27)	(3,326)
Total Unrealized Losses	(457)	(3,909)
Time in Continuous Loss, Fair Value
Less Than 12 Months Fair Value	124,283	180,785
12 Months or More Fair Value	8,813	209,752
Total Fair Value	$ 133,096	$ 390,537